Prokaryotic vs Eukaryotic Cells Cellular Hierarchy • Some organisms are unicellular (single celled); the cell carries out all life functions. Unicellular organisms are prokaryotic. • Multicellular organisms have many cells that work together to carry out life processes. • Tissues are groups of cells that perform the same function. Organs are several types of tissue working together to perform specific functions. Cell>Tissue>Organ>Organ System • An organ system is a group of organs working together for a particular function. For example, your digestive system breaks down food and puts it in the blood. Your circulatory system moves blood throughout your body. Your respiratory system puts O2 into your blood to be used by cells for respiration, and removes H20 and CO2. Organelles in unicellular organisms… • Work like the organ systems of multicellular organisms. • Each organelle has a specific function that helps keep the onecelled organism alive. Cell Membranes • Are found in ALL cells. • Help cell to maintain homeostasis (keeping a balance of solutes within a cell). • Are selectively permeable, meaning that only certain substances can go through in either direction. • Made of phospholipid bilayer. Passive Transport • Does NOT require energy. • Molecules move through the cell membrane from areas of higher concentration to areas of lower concentration. • There are 3 types of passive transport – diffusion, facilitated diffusion, and osmosis. Diffusion & Facilitated Diffusion • Diffusion is the process by which substances move directly through the cell membrane. • Facilitated diffusion involves the help of a carrier protein to move a substance from one side of the cell wall to the other. Osmosis • The movement of water from an area of high water concentration to an area of low water concentration through a semipermeable membrane. • Hypotonic has a lower concentration of solute (higher of water). • Hypertonic has a higher concentration of solute (lower of water). • Isotonic means the solute concentration is the same inside and outside the cell. Osmosis ALWAYS occurs from hypotonic to hypertonic… Active Transport • A process of moving material across the cell membrane from an area of low concentration to an area of high concentration • Requires energy to happen. • Exocytosis removes materials from a cell. • Endocytosis brings materials into a cell. The membrane “absorbs” the material. Factors Affecting Cellular Activity • Volume – cells with large internal volume cannot efficiently transport materials to the organelles that need them. • Surface Area – the greater the surface area, the more efficient the cell. • Environmental Factors – most cells function best within a specific range of temperature, light, and pH. (ex – plants) Fluid Pressure in Cells • Fluids are liquids and gases. Pressure is a force (push or pull) applied uniformly over an area. • Blood Pressure – pressure exerted by blood on the walls of blood vessels. • Turgor Pressure – pressure that plant cells put on each other when full of water; allows plants to stand up and move water up the stem or trunk to the top of the plant. Review • Unicellular organisms have one cell; multicellular have many. • Cells make tissues, which make organs, which make organ systems. • Organelles act as organs in a cell. • Passive transport (diffusion/osmosis) does not require energy. Active transport does. • Volume, surface area, and environmental factors (temperature, light, pH) affect cellular activity. • The amount of fluid pressure in a cell affects its efficiency.